Flip-flops that are data storage circuits can be used in various application fields. In a semiconductor circuit, a flip-flop stores or outputs at least 1-bit data, in synchronization with a clock signal.
Thus, flip-flops are circuits that have been widely used in semiconductor circuits, in the field of memory/non-memory. Recently, flip-flop circuits of a specific model have been laid out on a substrate and the layout of the flip-flop circuits has been unilaterally applied as a library to a semiconductor circuit.
In particular, since a plurality of flip-flops are used in a semiconductor circuit, a set of at least one flip-flop is applied as a layout on a substrate.
FIG. 1 is a block diagram of a library of conventional flip-flops provided using a general semiconductor design tool.
Referring to FIG. 1, four flip-flops FF1, FF2, FF3, and FF4 that perform specific functions form the same equivalent circuits, and layouts of the respective flip-flops are the same according to the same equivalent circuits.
A layout is a plan view of an aspect of a semiconductor circuit that is actually formed on a substrate. During an actual semiconductor design process, performing of a layout is indispensable to designing a transistor-level circuit and entering a manufacturing process. An exposure process is performed and an etch mask is manufactured, based on the layout. Thus, a transistor and a wiring pattern are formed on locations that are substantially identical to the layout, and are also shaped to be substantially identical to the layout.
FIG. 1 discloses the technique described above, in which a layout of a set of flip-flop circuits is the same as that of the other flip-flop circuits. Thus, in a semiconductor circuit, all of the layouts of the flip-flops FF1, FF2, FF3, and FF4 are the same. The layouts of the respective flip-flops are disposed adjacent to one another to form a set to flip-flops, and input/output lines thereof are connected during a subsequent wiring process.
When this structure is employed, a coupling capacitance occurs between adjacent flip-flops. The coupling capacitance causes cross-talk to occur in flip-flops that form a signal channel, thereby deteriorating a signal to be transmitted. Also, when a capacitor should be employed in flip-flops to adjust a signal transmission speed or a response rate, it is difficult to form a physical capacitor in the flip-flops that form a signal transmission path. This is because one flip-flop library is used and additional flip-flops thus cannot actually be laid out. In particular, when a plurality of flip-flops having the same shape are laid out and employed in a circuit, a soft error or the like inevitably occurs due to the cross-talk.
Also, a library provides a plurality of flip-flops of the same layout. Thus, when in various circuit constructions, impedance matching is needed due to different gates or circuits connected to an output terminal or an input terminal, additional matching means should be interposed between the flip-flops and a peripheral circuit. In general, as the matching means, a physical capacitance is artificially set or a capacitance is set using an additional transistor. In this case, diversity cannot be secured in selecting circuits during a semiconductor design process, and a burden on a manufacturing process is increased since an additional circuit is added.